High temperature stable viscosifier and fluid loss control system

ABSTRACT

The present invention is directed to a high temperature stable composition capable of imparting a combination of pseudoplasticity and fluid loss control properties to aqueous systems. The composition is a combination of: 
     (a) a hydroxy containing aluminum component 
     (b) a chemical compound capable of converting to a higher oxidation state under alkaline conditions; and 
     (c) a reaction product of a polymeric substance selected from polyvinyl alcohol or hydroxyalkyl cellulose reacted with at least 1 percent of stoichiometry of a cross-linking agent selected from an epihalohydrin or an aldehyde containing or generating agent; 
     wherein the amount of component (a) is at least 75 wt. percent of component (c) and component (b) is at least 25 wt. percent of component (c). 
     The invention is further directed to improved drilling fluids containing said composition and to the process of drilling bore holes using said improved fluid.

BACKGROUND OF THE INVENTION

The present invention relates to a composition which is capable ofimparting a high degree of non-Newtonian, pseudoplasticity and fluidloss controlling properties to aqueous systems and which is stable toelevated temperature conditions. More particularly, the presentinvention relates to the formation of an improved water-based, clay-freedrilling fluid containing the subject composition and to an improvedmethod of drilling bore holes into subterranean formations using saiddrilling fluid.

In normal well drilling operations in which a well is drilled by arotary method, the well bore hole is generally filled with a drillingfluid or mud which is circulated therein. Drilling fluids are usuallypumped down through the drill stem of the rotary rig, circulated aroundthe drill bit and returned to the surface through the annular passagebetween the drill stem and well wall. These drilling fluids perform anumber of functions including lubricating the drill stem and bit,cooling the bit, carrying the cuttings from the bit up the bore hole tothe surface where the cuttings may be separated and disposed of, andproviding a hydrostatic head against the walls of the well to containdownhole geopressure.

A primary requisite of a satisfactory drilling fluid is its ability toreadily circulate and flow, that is, to have low viscosity, under thehigh shear conditions which are present in the environs of the drill bitwhile, at the same time, being capable of having and maintainingsufficient viscosity to be capable of efficiently carrying the bitcuttings to the surface and maintaining in suspension, any other solidcomponents of the drilling fluid.

The drilling fluid must also be capable of inhibiting the amount offluid, normally water, which is lost into the porous strata throughwhich the bore hole traverses. The loss of fluid causes the formationand build-up of a cake deposit which, after a period of time, can causesticking of the drill pipe and stoppage of the drilling operation. Thedrilling fluid must, therefore, be of a nature which permits minimumloss into the porous strata. Agents which impart such property areconventionally termed "water loss controllers" or "fluid losscontrollers".

The drilling fluid must also be stable and functional after subjectionto elevated temperature conditions. In addition to the heat generated bythe frictional forces of the drill bit, it is well known that thetemperatures encountered in the bore hole are substantially above thatfound at the earth's surface. The deeper the bore hole is, the higherthe temperature encountered. Drilling to greater depths has becomecommon in today's quest for discovering new reserves. A general rule ofthumb indicates that for each 10° to 20° F. increase in temperaturestability one can use the same fluid to drill an additional 1000 ft. Itis, therefore, desired to produce a composition capable of exhibitingstability and desired functionality at the elevated temperaturescommonly encountered in deep drilling operations.

It is a widely held and accepted theory that the viscosities suitablefor creating a particle carrying capacity in the fluid can be achievedwith the drilling fluid having pseudoplastic properties. For example,the drilling fluid must be capable of having a low viscosity under thehigh shear rates such as encountered at the drill bit, yet have theability to increase in viscosity (and, therefore, particle holdingpower) under decreasing shear rates encountered in its upward movementthrough the annulus.

In order to obtain the requisite pseudoplastic properties, it has beenthought desirable to use clay or colloidal clay bodies such as sodiumbentonite. As a result, the drilling fluids have been usually referredto as "muds". The clay-based drilling fluids are, however, highlyunstable when they come in contact with various salts found in drilledearth formations.

Materials which have come into expanding use to impart rheologicalproperties to drilling compositions are xanthan gums such as aredescribed in U.S. Pat. Nos. 3,198,268; 3,208,526; 3,251,147; 3,243,000;3,307,016; 3,319,715 and 3,988,246. These materials have been found tocause aqueous solutions, such as drilling fluids, to exhibitpseudoplastic properties under varying low shear rates. However, thesematerials, whether used alone or in combination with other additives,present the problem of being irreversibly degraded by the elevatedtemperatures often encountered during conventional drilling operations.

Prior utilization of hydroxides or hydrated metal oxides of amphotericmetals in well treating fluids have involved properties distinctlydifferent from the properties required for a drilling fluid as describedherein. For example, U.S. Pat. Nos. 3,614,985 and 3,815,681 describe aprocess for plugging a subterranean reservoir by permeating its poreswith a solution containing an amphoteric metal salt and a pH increasingreactant to cause precipitation in the pores. U.S. Pat. No. 3,603,399describes a process for treating a water sensitive formation bypermeating its pores with a hydroxy-aluminum solution which is a clearand relatively non-viscous solution. In each of such prior well treatingprocesses, it has been important that the solution have relatively lowviscosity and high fluid loss to ensure that the solution penetratesinto the matrix or pores of the reservoir. Such fluids would not besuitable as a drilling mud. U.S. Pat. No. 3,860,070 describes a wellcompletion or fracturing fluid containing an amphoteric metal salt and abase in a ratio to make the final solution strongly acidic in order toform a thickened fluid suitable as a fracturing fluid. Such fluidscannot be used satisfactorily in a drilling operation due to theircorrosive nature with respect to the metal drilling equipment.

The viscosity of a drilling fluid has been relied upon as a mode ofaiding in fluid loss control with little success especially whendrilling into and through porous substrates. Various agents have beenadded to enhance the fluid loss properties of the mud. For example, U.S.Pat. No. 3,032,498 describes a cyanoethylated starch as a water losscontroller to be used in combination with a clay-based mud. U.S. Pat.Nos. 3,988,246 describes an esterified or etherified starch as a waterloss controlling agent which is compatible with a xanthan gum baseddrilling mud. Other agents as well as the starches mentioned above whichhave been employed in clay free muds to control fluid loss are generallyfound to be unstable to the temperature conditions encountered in deepwell drilling.

There is a general need for a composition which is capable of impartingboth pseudoplastic and water loss controlling properties to aqueouscompositions while being stable to varying conditions and elevatedtemperatures commonly encountered in deep drilling operations.

SUMMARY OF THE INVENTION

The present invention is directed to a high temperature stablecomposition capable of imparting a high degree of pseudoplasticity andfluid loss control to alkaline aqueous systems. The composition is acombination of:

(a) a hydroxy containing aluminum agent formed by mixing in an aqueoussolution and under a high degree of agitation a water soluble basicagent selected from an alkali metal aluminate, alkali metal hydroxide orammonium hydroxide with a water soluble acidic agent selected from aninorganic acid, or aluminum chloride, sulfate or nitrate such that atleast one of said agents is an aluminum containing compound;

(b) a chemical compound capable of converting to a higher oxidationstate under alkaline conditions; and

(c) a reaction product formed between a polymeric material selected frompolyvinyl alcohol or hydroxyalkyl cellulose and a cross-linking agent,the cross-linking agent present at a concentration equivalent to atleast about 1 percent of the hydroxyl groups present in the polymerreactant.

The subject combination imparts pseudoplasticity and fluid losscontrolling properties to an aqueous system which are unattributable toeach of the components and which are stable to elevated temperature andconditions commonly encountered in bore hole drilling operations.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a composition which is capable ofexhibiting stability under high temperature conditions, such as aboveabout 250° F. while imparting a high degree of pseudoplastic and fluid(commonly, water) loss controlling properties to aqueous systems; to theuse of such compositions to form an improved water-based, clay-freedrilling fluid; and to drilling of bore holes into subterraneanformations using said improved drilling fluid.

The subject composition is a combination of a hydroxy containingaluminum agent, a polymeric reaction product and a compound capable ofconverting to a higher oxidation state. The subject composition shall bedescribed in terms of its use as a component of a drilling fluid.

The hydroxy containing aluminum agents found useful as a component ofthe composition of the present invention are agents which aresubstantially water-insoluble, that is, agents which are in suspensionor dispersion in aqueous systems. Further, the subject hydroxycontaining aluminum agents can be characterized as having an X-raydiffraction spectrum containing a major characterizing diffraction peakat 6.3±0.2 Angstroms or characterized by an X-ray diffraction spectrumas being amorphous, that is, having substantially no X-ray diffractionpattern within the range of from 1.5 to 17 Angstroms. The spectrum isdetermined by standard techniques using the K-α doublet of copper as theradiation source.

The subject hydroxy containing aluminum agent of the subject inventionis formed by contacting certain acidic agents with certain basic agents,as described below, in an aqueous medium under a high degree ofagitation. The acidic and basic agents should be used in a ratio suchthat the resultant product is capable of imparting a pH of at least 8and preferably from 8 to 10.3 to the water medium in which it is formed.

The basic agents useful in forming the hydroxy-containing aluminumcomponent are water soluble basic materials selected from an alkalimetal aluminate, alkali metal hydroxide or ammonium hydroxide ormixtures thereof. Any alkali metal can be used, such as sodium,potassium and the like, with sodium being preferred.

The acidic agent useful in forming the hydroxy-containing aluminumcomponent are water soluble acidic materials selected from an inorganicacid as, for example, hydrochloric, sulfuric or nitric acid and thelike, or an aluminum salt selected from aluminum chloride, aluminumnitrate or aluminum sulfate, their hydrates or mixtures of these acidicagents. At least one and preferably both of the acidic and basic agentsmust be an aluminum containing agent. For example, the hydroxycontaining aluminum component may be formed from an alkali metalaluminate, such as sodium aluminate, and aluminum chloride hexahydratein an aqueous system. The sodium aluminate is mixed with the aluminumchloride hexahydrate in an aqueous phase under high speed mixing. Thealuminates which are useful normally will have an alkali metal oxide toaluminum oxide mole ratio of from about 1:1 to 2:1. These materials arecommercially available. If desired, solutions of one or both componentscan be made and then mixed together under high speed mixing to form thehydroxy containing aluminum agent.

The acidic and basic precursor agents can be present in concentrationsof from about 5 to 25 percent by weight based on the water present. Theconcentration can vary above the upper value indicated but should not besuch as to inhibit the thorough mixing, preferably under high speedagitation, of the agents during the formation of hydroxy-containingaluminum component. The acidic and basic agents can be mixed usingconventional equipment which can generate a high degree of agitation tothe aqueous medium. The ratio of acidic and basic component should besuch that a final pH of the aqueous medium is at least 8, is preferablyfrom 8 to about 10.3 and more preferably from about 8.3 to 9.7. Theresultant aluminum component has hydroxyl groups as an integral part ofits composition.

The polymeric component of the subject composition is formed bycontacting a polymeric material selected from a polyvinyl alcohol or ahydroxyalkyl cellulose, as fully described herein below, with acrosslinking agent selected from an aldehyde containing or generatingagent or an epihalohydrin.

The polyvinyl alcohol reaction product found useful in forming thesubject inventive composition is formed by contacting polyvinyl alcoholand an aldehyde containing or generating compound. The polyvinylalcohols found useful in forming the subject reaction product have aweight average molecular weight of at least about 20,000 and preferablythe weight average molecular weight should be from about 90,000 to200,000. Conventionally polyvinyl alcohol is the hydrolyzed product ofpolyvinyl acetate. The hydrolysis should be at least about 75 percentcomplete and preferably from about 80 to 95 percent complete to form asuitable polyvinyl alcohol reactant. The polyvinyl alcohol reactant,such as formed from the hydrolysis of polyvinyl acetate or the like, canbe reacted in an aqueous medium with an aldehyde containing orgenerating reactant. Suitable aldehyde containing reactants include, forexample, formaldehyde, acetaldehyde, propionaldehyde, glycolaldehyde,glyoxylic acid and the like or polyaldehydes such as glyoxal,glutaraldehyde, paraformaldehyde and the like. Other suitable aldehydereactants include aldehyde generating agents such asmelamine-formaldehyde monomeric products and derivatives such as tri andhexa(methylol)melamine and the tri and hexa(C₁ -C₃alkoxymethyl)melamine. Such materials can be formed by knownconventional methods. The alkyl blocked derivatives are commerciallyavailable, are stable to self polymerization and are, therefore,preferred. Of all of the aldehyde reactants, the preferred reactants areparaformaldehyde and formaldehyde.

The cross-linking agent found suitable in forming the subjectcross-linked polyvinyl alcohol component can also be an epihalohydrin.The halo group can be chlorine, bromine and the like with chlorine beingpreferred. Further, the epihalohydrin can be substituted with a C₁ -C₃alkyl group such as methyl, ethyl, or propyl. The most preferredepihalohydrin cross-linking agent is epichlorohydrin due to itsavailability and superior product formed.

The subject polyvinyl alcohol reaction product found suitable in thesubject composition to impart the combined desired properties can beformed by reacting a polyvinyl alcohol, as described above, with from atleast about 1 and preferably from about 1 to 200 and most preferably 2to 50 percent of stoichiometry of at least one of the above describedcross-linking reactants based on the hydroxyl contant of the polyvinylalcohol. We define stoichiometry as the reaction of 2 OH groups with onealdehyde or epi group. Excess cross-linking reactant can be used. Theparticular quantity of reactant will depend upon the solubility of thereactant in the aqueous reaction media, its reactivity and the likeproperties as is conventional to those skilled in this art. The reactionproduct should be dispersible in water. The reaction to form thepolyvinyl alcohol-aldehyde reaction product can be carried out in anaqueous medium which should be acidic, that is, have a pH of 5.5 or lessand preferably from 1 to 4.5 and which may contain other components,such as alkali metal sulfates in from 1% to saturation, to aid in theformation of the polymer product. The reaction can be carried out atambient or elevated temperatures, such as from about 50° C. to 100° C.The solid product can be recovered by conventional techniques such as bysalting out the product using suitable salts as, for example, sulfate,carbonate or phosphate salts, decantation, filtration and drying.

The hydroxyalkyl cellulose reaction product found useful in forming thesubject inventive composition is formed by contacting a hydroxyalkylcellulose with a cross-linking agent as described below. Thehydroxyalkyl cellulose can have a C₁ -C₃ alkyl group and, therefore, behydroxymethyl, hydroxyethyl, hydroxy-n-propyl or hydroxyisopropylcellulose. These materials are commercially available. The preferredmaterial is hydroxyethyl cellulose. It is well known that unmodifiedcellulose chains are composed of repeating anhydroglucose rings, each ofwhich has three hydroxy groups. To form hydroxyethyl cellulose, forexample, the cellulose is conventionally treated with an alkalihydroxide and then reacted with ethylene oxide by known manners. Thehydroxyalkyl cellulose can have a weight average molecular weight of atleast about 20,000 and preferably at least 60,000 with from 60,000 to150,000 being most preferred.

The cross-linked hydroxyalkyl cellulose suitable in the presentinvention can be formed by reacting hydroxyalkyl cellulose with across-linking agent selected from an aldehyde or aldehyde generatingagent or an epihalohydrin. Suitable aldehyde containing reactants oraldehyde generating agents or epihalohydrins are those agents describedherein above as reactants with polyvinyl alcohol.

The subject cross-linked hydroxyalkyl cellulose can be formed byreacting a hydroxyalkyl cellulose, as described above, with from atleast about 1 and preferably from about 1 to 200 and most preferably 2to 50 percent of stoichiometry of a cross-linking reactant.Stoichiometry is based on all three available hydroxyl groups of theanhydroglucose rings forming the hydroxyalkyl cellulose.

The formation of the cross-linked hydroxyalkyl cellulose with analdehyde is carried out in an aqueous acidic medium which has a pH of5.5 or less and preferably from 1 to 4.5. The reaction can be carriedout at ambient or elevated temperatures, such as from about 50° C. to100° C. The solid product can be recovered by conventional techniques ofprecipitation by salts or alcohol, filtration and drying.

The formation of the cross-linked hydroxyalkyl cellulose and thecross-linked polyvinyl alcohol with an epihalohydrin should be carriedout in a basic aqueous medium which has a pH of at least about 9.5. Thereaction can be carried out at ambient or elevated temperatures, such asfrom about 50° C. to 100° C. The product is recovered by conventionaltechniques of precipitation by salts of alcohol, filtration and drying.

The present invention further requires the use of a compound capable ofconverting from a lower to a higher oxidation state. The ability of thecompound to make such a conversion is not meant to limit the inventionto the requirement that the subject compound undergoes such conversionor that the agent, per se, is merely the precursor for the productrequired in the subject composition. The compound can be organic orinorganic and of momomeric, low molecular weight. Organic compoundswhich are suitable include alkanols, preferably lower alkanols, as, forexample, methanol, ethanol, n-propanol, iso-propanol, butanols andpentanols and the like; phenols such as phenol, C₁ -C₃ alkyl, aryl andalkaryl substituted phenols, tert-butylcatechol and hydroquinone and thelike; mercaptans such as C₁ -C₁₅ alkanethiols and the like. In additionthe agent can be an inorganic readily oxidizable substance such as analkali metal or alkaline earth metal or ammonium salt of sulfite,bisulfite, thiosulfate, hydrosulfite or nitrite; ferrous or cuprousmetal salts of chloride, sulfate and alkali metal borohydrides and thelike and their equivalence. The preferred materials are water soluble C₁-C₅ alkanols, sulfite salts, bisulfite salts and nitrite salts of analkali or alkaline earth metal or ammonium.

The components of the subject composition should be present in effectiveamounts such that, in combination, they are capable of exhibiting a highdegree of pseudoplasticity and fluid loss controlling properties.Normally the combined properties are attained by using the abovedescribed hydroxy containing aluminum agent and polymeric reactionproduct in amounts such that their weight ratio is at least 0.75 to 1with ratio of from 0.75:1 to 3:1 being preferred and 1:1 to 3:1 beingmost preferred. The chemical compound capable of converting to a higheroxidation state described herein above should be used in amounts suchthat the ratio of the chemical compound to polymeric reaction product isat least 0.2:1 with, preferably, a ratio of 0.2:1 to 1:1 and mostpreferably a ratio of at least 0.25:1 to 0.75:1.

Compositions having the combination of the above described componentshave unexpectedly been found to exhibit the desired combination ofproperties of pseudoplasticity and fluid-loss control which areunattainable by separate use of the materials. Further, the compositionis capable of maintaining these properties under elevated temperaturesfound in deep bore hole drilling such as greater than 250° F. (121° C.)and generally are stable at temperatures of 300° F. (149° C.) andgreater.

Amphoteric metal hydroxides formed in various manners and from variousmaterial are known to form a gelatinous mass in aqueous systems. Aqueousamphoteric metal hydroxide gels have been found useful for variouspurposes, such as coatings, adhesives and the like as well as inspecific well treating compositions, such as fracturing or completionfluids. Such gels and compositions are used under conditions distinctlydifferent than presently required and do not exhibit water-losscontrolling properties. Although hydroxy-containing aluminum agentsdisclosed herein have been unexpectedly found capable, when used alone,of imparting a certain degree of pseudoplasticity to aqueous systems,they do not impart fluid loss control to aqueous systems.

The presently described polymeric reaction products do not, when usedalone, exhibit and impart fluid loss control or pseudoplasticity asdescribed herein above to aqueous systems such as water-based clay-freedrilling fluids.

The aqueous system which contains the subject composition should have analkaline pH of at least 8 and preferably from 8 to 12 and morepreferably of from 8.3 to 10.3. At these alkaline pH conditions, oneattains the desired properties. Adjustment of the pH can be done withany water soluble inorganic base or acid such as alkali metal hydroxide,alkaline earth metal hydroxide or a hydrohalic acid, sulfuric acid,nitric acid, sodium bicarbonate, or sodium carbonate.

The aqueous system should be mixed to the extent required to cause thecomponents of the composition to be substantially uniformly distributedtherein. Further, the hydroxy aluminum containing aqueous medium orpreferably the resultant composition containing system may have thecombined described pseudoplastic and fluid loss control propertiesfurther enhanced by subjecting the system to mixing at high shear ratesof about 20,000 sec.⁻¹ or greater for short periods of time such as from5 to 60 minutes as by circulating the aqueous system through a smallinternal diameter tube at high rate.

The aqueous medium in which the above-described hydroxy-containingaluminum agent is formed can be directly used to form the water-baseddrilling fluids of the subject invention. The aqueous medium can bediluted with sufficient amount of water to form a system having fromabout 1 to 15 percent, and preferably from 1.5 to 10 weight percent ofthe subject composition therein. The concentration most suitable can bereadily determined in conventional manners by the mud engineer takinginto consideration the concentration and nature of other materials whichmay also be contained in the drilling fluid.

The above-described composition is capable of imparting to a clay-free,(the term "clay-free" when used herein refers to the absence of drillingfluid viscosifying clays as an essential agent of the fluid and not toother materials entrained therein) aqueous system, such as a water-baseddrilling fluid (the term "fluid" or "system" when used herein refers towater-based systems containing the subject composition) non-Newtonian,pseudoplasticity, that is to say, that the viscosity of the resultantfluid varies inversely with respect to the shear rate exerted on thefluid. The relationship of the shear stress with respect to shear ratecan be defined by the rheological power law model relationship of

    τ=K(γ).sup.n

in which τ represents the shear stress exerted on the aqueous system ofthe drilling fluid in units such as pounds per 100 ft² or dynes/cm² ; γis the shear rate in units of reciprocal time such as sec⁻¹ ; K is aconstant having the value of the shear stress of the particular aqueoussystem at a shear rate of 1 sec⁻¹ ; and n is a numerical value greaterthan zero. When n=1, the system is Newtonian; if n is less than 1, thesystem is pseudoplastic, and if n is greater than 1, the system isdilatant. It has been unexpectedly found that fluids containing thepresently described composition exhibit shear stress (τ) properties atvarying shear rates (γ) in the range of from about 10 to 400 sec⁻¹, thatis, in the range normally encountered in the annular region of the borehole such that n of the power law relationship has a value of less thanabout 0.4. Such systems, therefore, exhibit non-Newtonian, pseudoplasticproperties to an exceptionally high and desirable degree.

The above-described composition has been unexpectedly found to exhibit ahigh degree of fluid loss control. That is to say that the fluid iscapable of interacting with the adjacent porosity to inhibit loss of thefluid to the porous environment. The fluid loss of the system can bedetermined in accordance with the American Petroleum Institute'sprocedure API No RP-13B. After initial spurt, the desired water losscontrol normally attained with the subject composition is of less thanabout 20 ml per 30 minutes.

The drilling fluids containing the subject composition have unexpectedlybeen found to have high degrees of stability with respect to theirrheological and fluid loss properties under various adverse conditions.Such fluids have been found to be stable after subjection to elevatedtemperatures for sustained periods of time, to high shear rates such asare encountered at the site of the drill bit, as well as being stable inthe presence of various corrosive elements such as calcium chloride, andsodium chloride which may be entrained in such fluids.

The high degree and breadth of stability of the presently achieveddrilling fluid, when combined with its ability to exhibit non-Newtonian,pseudoplastic properties under varying low shear rates of from about 10to 400 sec⁻¹ and greater, such as are encountered in the annular regionbetween the drill stem and the casing of the bore hole, aids inincreasing the drilling efficiency, that is, the rate of drilling thebore hole.

The drilling fluid composition of the subject invention can containother conventional drilling fluid additives such as weighting agents as,for example, crushed oyster shells, barite and the like; thinner such asferrochrome lignosulfonate and the like; lost-circulation agents such asground walnut shells, cotton seed hulls and the like; pH adjusters suchas MgO, sodium carbonate, sodium bicarbonate and the like; as well asother conventional additives.

The terms "water-based" or "aqueous-based" which are used herein indescribing the present invention, generally includes drilling fluidswhich have a liquid base comprising substantially fresh water or saltwater. However, it is to be realized that at times certain small amountsof other liquids may be emulsified or admixed with the water-basedfluid. For example, drilling fluids may at times contain small amountsof oil, emulsified or admixed with the drilling fluid, the oil comingeither from an oil bearing formation which has been drilled into or,under certain conditions, from purposeful addition.

The present water-based, clay-free drilling fluids containing thesubject composition have been found to be stable to elevatedtemperatures such as greater than 250° F. to about 350° F. encounteredin deep well drilling, the presence of calcium and sodium salts and tothe presence of conventional drilling fluid additives. Otherviscosifiers and water loss controllers need not be present. Further,the present drilling fluids are substantially non-corrosive andnon-destructive to metal equipment commonly used in drilling operations.

The subject composition can be used with conventional bore hole drillingequipment in manners known to those skilled in the art to efficientlyand effectively drill bore holes into subterranean formations. Thepseudoplastic and fluid loss control properties of drilling fluidscontaining said composition permit effective removal of the cuttingsfrom the area at and around the drill bit to permit more efficientdrilling of the formation when circulating the fluid during bore holedrilling.

The following examples are given for illustrative purposes only, and arenot meant to be a limitation on the subject invention except asindicated by the appended claims. All parts and percentages are byweight unless otherwise indicated. The units of K of the power law islb-sec/100 ft².

EXAMPLE I Formation of Cross-Linked Hydroxyethyl Cellulose

A. A 40 percent aqueous solution of glyoxal was added with stirring to a5 percent solution of a commercially obtained hydroxyethyl cellulose (MSequals 2.5; Brookfield viscosity of a 5 percent aqueous solution equals150 centipoise) (Natrosol 250L). The weight ratio of glyoxal tohydroxyethyl cellulose was 21 to 100. The pH of the aqueous system wasadjusted to 3.5 with 1 N HCl and the system was heated to 60°-70° C. for30 minutes with stirring. The resultant aqueous suspension ofcross-linked hydroxyethyl cellulose was adjusted to pH 9.5 with 10percent NaOH solution.

B. A cross-linked hydroxyethyl cellulose was made in the same manner asin Part A above, except that paraformaldehyde was used instead ofglyoxal. The weight ratio of paraformaldehyde to HEC was 13.5 to 100.

C. A cross-linked hydroxyethyl cellulose was prepared by adding 5.1parts epichlorohydrin and 4.4 parts sodium hydroxide to 200 parts of a 5percent aqueous solution of hydroxyethyl cellulose, as described above.The solution was heated to 80° C. and maintained at that temperature for1 hour under continuous agitation. The material was cooled to form theaqueous suspension of cross-linked hydroxyethyl cellulose.

Formation of Polyvinyl Alcohol/Aldehyde Product

200 parts of a commercially obtained polyvinyl alcohol having weightaverage molecular weight of 125,000 and 87% hydrolyzed (Gelvatol 20-90)were dispersed in 600 parts of a 16 percent Na₂ SO₄ aqueous solution.The solution was then adjusted to pH of 3.0 with HCl. The mixture washeated to 50° C. with stirring. 68 parts of paraformaldehyde were addedand then the temperature was raised and maintained for 30 minutes at thetemperature of 60° C. while maintaining slow stirring. The mixture wascooled and adjusted to pH of 9.5 with NaOH. The resultant product wasfiltered air dried and then dried at 50° C. under vacuum for 16 hours.

Formation of Hydroxy-Containing Aluminum Agent

15.3 parts of commercially obtained sodium aluminate (Na₂ O.Al₂ O₃.3H₂O) powder was mixed with 12.2 parts of commercially obtained aluminumchloride hexahydrate powder. The mixture was added to 350 parts waterand subjected to high speed mixing using a Hamilton Beach Model 936-2mixer for 20 minutes. The aqueous dispersion was allowed to sit for 18hours and then again subjected to high speed mixing for 5 minutes. ThepH of the resultant dispersion was 8.5 and was adjusted to 9.6 withdilute NaOH.

The hydroxy-containing aluminum agent concentrations will be determinedherein below based on the formula A10(OH) although the subject agent maybe present in other forms.

EXAMPLE II

For comparative purposes, aqueous samples of hydroxy-containing aluminumand of each of the polymeric reaction products, respectively, weretested for rheology and fluid loss control.

An aqueous system having 3 percent of the hydroxy-containing aluminumproduct prepared according to Example I above and having a pH of 9.6 wassubjected to rheological analysis using standard procedures with a HaakeRotovisco RV-1 rotating rheometer at varying shear rates of from 8 to800 sec⁻¹ and at 25° C. The values determined for n and K in accordancewith the power law model relationship was 0.19 and 2.3, respectively.The fluid loss control of the material was determined using AmericanPetroleum Institute (API) procedure RP 13B at 100 psi and 25° C. A fluidloss value of greater than 150 ml/30 minutes was obtained. The productimparted good pseudoplasticity but substantially no fluid loss control.

The cross-linked hydroxyethyl cellulose product of Example I was dilutedwith water to form aqueous systems having 1 percent cross-linkedhydroxyethyl cellulose therein. The rheology and fluid loss controlproperties were determined in the same manner and procedures describedherein above with respect to the hydroxy-containing aluminum compound.The material was found to be substantially Newtonian (n=1, K=<0.1), andto have a fluid loss of greater than 100 ml/30 minutes. The cross-linkedHEC reaction products do not impart pseudoplasticity or fluid losscontrol to aqueous systems.

The polyvinyl alcohol/paraformaldehyde products of Example I werediluted with water to form aqueous systems having 1.5 percent PVA/A. Therheology and fluid loss control were determined in the same manner andprocedures described with respect to the hydroxy-containing aluminumcompound herein above. The materials were found to be Newtonian (n=1,K=<0.1), and to have a fluid loss of greater than 200 ml/30 minutes. ThePVA/A reaction products do not impart pseudoplasticity nor fluid losscontrol.

EXAMPLE III

This example illustrates that aqueous systems containing a compositionof the hydroxy containing aluminum compound, a polymeric reactionproduct (PVA/A) and a compound capable of converting to a higheroxidation state forms a system having pseudoplasticity and water losscontrol even when subjected to high temperature conditions.

An aqueous system was formed by mixing 4 parts of the hydroxy aluminummaterial (2.4 percent of system) formed in Example I above with 1 partof an 8% dispersion of the polyvinyl alcohol reaction product (1.6percent of system) formed in Example I above and with 0.025 partmethanol (0.5% of system). The pH of the resultant system was adjustedto pH of 9.5. A sample (III-1) of the system was subjected torheological and fluid loss control properties. The rheological analysiswas conducted using standard procedures with a Haake Rotovisco RV-1rotating rheometer at varying shear rates of from 8 to 800 sec⁻¹ and at25° C. The values of n and K were determined in accordance with thepower law model relationship τ=K(γ)^(n) in which is in units of lbs/100ft² ; γ is in sec⁻¹ ; K is in units of lb-sec/100 ft² ; and n is anumerical value of from 0 to 1 with values of less than 0.4 indicatinggood pseudoplastic properties. A second sample (III-2) taken from theformed system was placed in a vessel under N₂ atmosphere, sealed andsubject to 149° C. (300° F.) for 16 hours while under constant agitationand then allowed to cool to room temperature. The rheology and fluidloss control of the heat treated composition were determined by theabove referenced procedure. Finally, a third sample (III-3) of thecomposition was subjected to elevated temperature (300° F./16 hours) andwas then subjected to high shear forces by circulating the samplecomposition through a capillary tube (I.D.=0.0314 inch) for 30 minutesto give an approximate calculated shear rate of 25,000 sec⁻¹. The fluidloss control was determined according to API procedure RP 13B andrecorded as corrected fluid loss (CFL in ml/30 min. The corrected fluidloss is obtained by substracting the spurt value from the total fluidloss volume. The corrected fluid loss value is the rate of loss thefluid would be expected to exhibit over an extended period. The rheologyand fluid loss control of this sample were determined. A summary of theresults are contained in Table I below.

                  TABLE I                                                         ______________________________________                                        Sample    n             K      CFL                                            ______________________________________                                        III-1     0.23          8.0    7.6                                            III-2     0.18          17.0   11.0                                           III-3     0.19          18.0   11.2                                           ______________________________________                                    

The results show that the system exhibits good stability with respect torheology and fluid loss control even after subjected to very hightemperature and shear force conditions.

EXAMPLE IV

An aqueous system was formed and tested in the same manner as describedin Example III above except that one half part of ground limestone (<200mesh U.S. Std.) was added and mixed into each of the samples aftertreatment but prior to testing. The limestone simulates rock cuttings asare encountered by drilling muds in bore hole formation. The results areshown in Table II below:

                  TABLE II                                                        ______________________________________                                        Sample    n             K      CFL                                            ______________________________________                                        IV-1      0.26          6.1    8.8                                            IV-2      0.19          20.0   8.5                                            IV-3      0.24          22.0   8.3                                            ______________________________________                                    

The test results clearly indicate that the formed system maintains itsrheological and fluid loss control properties and is stable to veryelevated temperatures as encountered in deep bore hole drillingoperations.

EXAMPLE V

A sample was formed and tested in the same manner as described inExample IV above except that an equivalent weight percent of sodiumsulfite was used instead of methanol. The results given in Table IIIagain shows that the subject composition imparts rheology and fluid lossproperties which are stable even after subjection to extreme elevatedtemperatures and shear forces.

                  TABLE III                                                       ______________________________________                                        Sample    n             K      CFL                                            ______________________________________                                        V-1       0.24          5.4    8.2                                            V-2       0.18          20.0   8.8                                            V-3       0.22          22.0   8.2                                            ______________________________________                                    

EXAMPLE VI

An aqueous system is formed in the same manner as described in ExampleIII except that the hydroxyethyl cellulose reaction product in Example Iis used instead of the polyvinyl alcohol reaction product. Samples ofthe formed system are tested as described in Example III and show goodrheology and fluid loss control properties similar to that attained inExample III above.

EXAMPLE VII

A comparative system was prepared in the same manner as described inExample III above except that no compound (i.e. methanol) capable ofconverting to a higher oxidation state was included in the formedsystem. Samples of the system were tested as described in Example IIIabove. The results are given in Table IV below.

                  TABLE IV                                                        ______________________________________                                        Sample   n            K      CFL                                              ______________________________________                                        VII-1    0.20         7.4    8.2                                              VII-2    0.20         10.9   410.                                             VII-3    0.18         12.9   >200.                                            ______________________________________                                    

The results clearly show that samples which did not contain a compoundcapable of converting to a higher oxidation state were unstable and notcapable of exhibiting the desired properties after being subjected to anelevated temperature of 300° F.

We claim:
 1. A composition capable of imparting to clay-free aqueoussystems a combination of pseudoplasticity and fluid loss controlcomprising a mixture of:(a) a hydroxy containing aluminum componentformed by mixing in an aqueous medium and under a high degree ofagitation a water-soluble basic agent selected from the group consistingof an alkali metal aluminate, alkali metal hydroxide, ammonium hydroxideand mixtures thereof with a water-soluble acidic agent selected from aninorganic acid, aluminum chloride, aluminum sulfate, aluminum nitrate,their hydrates and mixtures thereof; at least one of said basic andacidic agents being an aluminum containing compound: said acidic andbasic agents being reacted in a ratio such that the resultant product iscapable of imparting to an aqueous medium a pH of at least about 8; incombination with (b) a chemical compound capable of converting to ahigher oxidation state under alkaline conditions selected from the groupconsisting of C₁ -C₅ alkanols, unsubstituted or C₁ -C₃ alkyl, aryl oralkaryl substituted phenols, hydroquinone, C₁ -C₁₅ alkanothiol, alkalimetal, alkaline earth metal or ammonium salt of sulfite, bisulfite ornitrite, ferrous metal salts of chloride or sulfate and cuprous metalsalts of chloride and sulfate; in combination with (c) a reactionproduct formed between a polymeric material having a weight averagemolecular weight of at least about 20,000 selected from the groupconsisting of polyvinyl alcohol and hydroxy C₁ -C₃ alkyl cellulose andat least from about 1 to 200 percent of stoichiometry of a cross-linkingagent selected from the group consisting of a compound containing atleast one aldehyde group therein or a compound capable of generating insitu at least one aldehyde or an epihalohydrin; the reaction betweensaid polymeric material and said aldehyde carried out in an aqueousacidic medium having a pH of 5.5 or less and the reaction between saidpolymer and said epihalohydrin being carried out in an aqueous basicmedium having a pH of at least about 9.5;wherein the weight ratio ofcomponent (a) to (c) is at least from about 0.75:1 to 3:1 and ofcomponent (b) to (c) is at least from about 0.2:1 to 1:1.
 2. Thecomposition of claim 1 wherein the aldehyde containing or generatingagent of (c) is selected from the group consisting of formaldehyde,acetaldehyde, propionaldehyde, glycolaldehyde, glyoxylic acid, glyoxal,glutaraldehyde, paraformaldehyde, trimethylol melamine, hexamethylolmelamine, tri(C₁ -C₃ alkoxymethyl) melamine or hexa(C₁ -C₃ alkoxymethyl)melamine.
 3. The composition of claim 1 wherein the mixture is dispersedin an aqueous medium.
 4. The composition of claim 1 wherein component(b) is selected from the group consisting of C₁ to C₅ alkanols, alkalimetal, alkaline earth metal or ammonium salts of sulfite, bisulfite ornitrite or mixtures thereof.
 5. The composition of claim 1, wherein thecomponent (c) is formed from polyvinyl alcohol having a weight averagemolecular weight of from about 90,000 to 200,000 and at least about 75percent hydrolyzed and the ratio of (a) to (c) is from about 1:1 to 3:1.6. In a water-based, clay-free drilling fluid suitable for circulatingin a bore hole while drilling the bore hole into subterranean formationswhich includes, water, a weighting agent, a rheology enhancing agent anda fluid-loss controller, the improvement comprising that said rheologyenhancing agent and fluid-loss controlling agent are, in combination,the composition of claim 1, 2, 3, 4 or 5 present in said fluid in fromabout 1 to 15 percent by weight based on the weight of the water presentin said fluid and said fluid is maintained at a pH of from about 8 to11.5.
 7. In a process of drilling a bore hole into a subterraneanformation using conventional bore hole drilling equipment, theimprovement comprising circulating in the bore hole while drilling thedrilling fluid of claim 6.